It is well known to continuously monitor one or more physiological conditions of certain subjects of clinical studies, athlete s or medical patients. The monitored conditions may include, but are not limited to, ECG activity, pulse rate, respiration rate, body temperature and blood pressure.
Today's medical patient monitoring systems, for example, are highly sophisticated telemetry systems particularly at the central receiving or monitoring stations. Indeed, medical technology has progressed to the point where central monitoring stations now consist of mainframes with interchangeable receiver modules that can be updated to avoid obsolescence. These modules receive and record such individual physiological parameters as ECG signals, arterial and pulmonary arterial characteristics, central venous pressure dynamics and peripheral pulse oximetric data.
While recent research and development has focused on state-of-the-art mainframe and module improvements, relatively little research has been directed toward improving input systems (transmitters) located at the patient-system interface. These transmitters are used to detect physiological parameters (most commonly ECG signals) and send these signals via radio frequency to the central receiving stations. It is not uncommon to have thirty (30) or more receiving monitors in operation simultaneously in an average sized hospital.
Conventional single channel ECG telemetry transmitter units normally consist of three major components:
1. Three (3) independent electrodes or sensors PA1 2. Three (3) lead cables PA1 3. Transmitter and battery pack
Hospitalized patients that require ECG telemetry monitoring thus must endure the encumbrances of elongated cables (usually three to five feet in length) that independently connect generally three ECG sensor electrodes to a transmitter and battery pack housing. Typical electrode patches are approximately two inches in diameter, usually circular, and adhere to the skin firmly with biologically compatible adhesive. They are conventionally placed just below the left and right shoulder and the left side of the upper abdomen at an approximate distance of between about 15 to 20 inches for a typical adult patient. The cables are commonly run through the patient's shirt sleeve or beneath the bed clothing. The transmitter and battery pack housings are formed as a plastic case measuring approximately 4.times.7.times.1.5 inches and are placed in paper pouches that are attached to the patient's clothing with a safety pin or the like. With a transmitter unit so constructed and arranged, the patient is burdened by the bulky transmitter housing and the lead cables that are apt to be caught on bed rails, lavatory equipment, food trays, IV poles and other objects regularly encountered by the patient. Additionally, the cables are prone to entangle and dislodge from the patient, thereby interrupting signal transmission.
Further, when a patient is undergoing an operation, a mainframe monitor is permanently stationed in the operating room for enabling the anesthesiologist to monitor vital signs such as heart rate and ECG signals. Upon completion of the operation, the patient is placed upon a transportable bed and moved to a recovery area. It is during this transportation that the sensor lead cable connections of conventional systems often become dislodged or entangle with other wires or intravenous (IV) tubing. Additionally, a rather large and heavy monitor must accompany the patient, thereby compounding the difficulties attendant to this delicate postoperative patient transport period.
Examples of ECG monitoring systems which describe sophisticated developments in mainframe technology can be found in U.S. Pat. Nos. 3,832,994, 4,981,141, 5,025,808 and 5,036,869. These patents, however, provide little disclosure as to the construction or operation of their patient-carried ECG sensors. Additionally, each recite conventional practice as to sensor placement on the patient's body, i.e., widely separated across the patient's torso or, in the case of U.S. Pat. No. 5,025,808, on the patient's arms and legs.
U.S. Pat. Nos. 3,972,320, 4,494,553, 4,889,131 and 4,819,860 represent various endeavors in physiological monitoring system apparatus particularly directed to the remote sensors carried by the patient. Of these, U.S. Pat. No. 3,972,330 and 4,819,860 teach of wrist-carried sensors which transmit to a central receiving station data signals corresponding to detected physiological conditions; whereas, U.S. Pat. No. 4,494,553 and 4,889,131 each describe belt-like sensor equipment that is worn about a user's torso.
U.S. Pat. No. 3,253,588 describes user-carried physiological sensors of complex construction and operation. The sensors include not only means for detecting a particular physiological condition, but also means for receiving an interrogation signal from a remote station and means responsive to the interrogation signal for transmitting to the remote station a signal corresponding to the detected physiological condition.
U.S. Pat. No. 3,943,918 discloses a disposable physiological telemetric sensor including microcircuitry, wiring and multiple electrodes and batteries, all at which are discarded after a single use of the sensor. As will be appreciated, the waste attendant to disposal of the sensors and the many internal electrical components thereof after a single application renders usage of Such sensors somewhat impractical and economically unattractive from the perspective of large-scale users of such equipment, e.g., health care providers such as hospitals, clinics and nursing homes.
An advantage exists, therefore, for a telemetric physiological condition (particularly an ECG signal) sensing and transmitting unit that is compact, unobtrusive to the wearer, uncomplicated in design, and offers comparatively inexpensive and reliable long-term service. A further advantage exists for a system incorporating such a sensing and transmitting unit and a lightweight and completely portable receiver unit capable of displaying in real-time visual information corresponding to the patient's physiological signals,